Field of the Invention
The field of the invention is inhalers. More specifically, the invention relates to dry powder inhalers for delivering drugs in a finely divided dry powder or fluid form.
Inhalers are used to deliver drugs into a patient's lungs. Typically, an inhaler contains or provides a mixture of drugs and air or propellants. The mixture is delivered via the patient inhaling from a mouthpiece on the inhaler, for treatment of various conditions, for example, bronchial asthma. However, delivery of drugs via inhalation can be used for many other treatments, including those unrelated to lung conditions.
One well known inhaler, described in PCT application No. PCT/US93/09751 contains individual medicine doses stored within a plurality of apertures in a medicine containing cartridge. The cartridge is manually advanced to successive doses by rotating the medicine containing cartridge. However, while the above-described device has met with varying degrees of success, disadvantages still remain in indexing or advancing the cartridge within the inhaler, and in reliably delivering a precise quantity of drug from the cartridge.
U.S. Pat. Nos. 5,327,883, and 5,577,497, both incorporated herein by reference, describe an inhaler having a spinning impeller. The motor for spinning the impeller is switched on by a sail-switch. In the above design, the sail switch has a sail or flap which is moved by the flow of air caused by the patient inhaling. The mechanical movement of the flap closes the switch, thereby turning on the motor. The motor spins an impeller within a mixing chamber, resulting in drug/air mixing and drug particle deagglomeration. As the inhaler is substantially flow rate independent, and may be used at very low flow rates, the switch must be very sensitive to air flow. Although the sail-switch has performed well in the past, improvements remain to be made in switch performance.
Inhalers have also used various techniques for storing drugs to be delivered. Some inhalers have used bulk drug storage reservoirs and mechanisms for dividing out individual doses with each use. Other inhalers have used separately packaged drug doses, such as in U.S. Pat. Nos. 4,778,054 and 5,327,883. Still, reliable and consistent delivery of doses of dry powder drugs has remained as an elusive objective.
Accordingly, it is an object of the invention to provide an improved inhaler.